The present application relates generally to antenna systems in portable electronics devices having two or more antennas operating simultaneously.
Portable electronics devices (e.g., USB Dongles and other wireless routers, cellular handsets, personal digital assistants, smart phones, and portable personal computers) typically include electronics components on a printed circuit board (PCB) assembly. Antennas for radio communications to and from such a device may be attached to the PCB assembly. For example, single-ended antennas may be fed directly from the PCB assembly, which then serves as a counterpoise for the antennas, allowing the antennas to be much smaller than otherwise possible. When the counterpoise is small (e.g., with dimensions on the order of the operating wavelength of the antennas or less), feeding two or more antennas from the same counterpoise can have the disadvantage of introducing too much coupling from one antenna to another. This is an example of a coexistence problem where more than one radio must operate at the same time from the same device.
One example of a device having two or more antennas fed from the same counterpoise is a portable wireless router device using a first radio for communication with a wide area network (WAN) using WiMAX in the 2500 to 2700 MHz band, and a second radio for local area network (LAN) communication using 802.11 (WiFi) protocols in the 2400 to 2500 MHz band. It is desirable to obtain as much isolation as possible between the antenna(s) connected to the WiMAX radio and the antenna(s) connected to the WiFi radio because the adjacent operating bands make the radios particularly vulnerable to interfering with each other.
Additionally, industrial design trends for portable electronics devices are driving slimmer form factors. At the same time, advanced communications systems using multiple-input, multiple-output (MIMO) signal processing techniques are driving multiple radio transmitters onto these platforms. The combination of two or more radios and a slim form factor creates significant difficulties in meeting Specific Absorption Rate (SAR) regulatory requirements.